Improve deployment concurrency GCL management

[collincchoy]

Closes #15375

This PR includes several changes to support shifting the int-based Deployment.concurrency_limit over to a foreign key relationship between Deployment and ConcurrencyLimitV2 in order to centralize the source of truth for a deployment's concurrency limit value.

More specifically, this PR:

• Adds a new deployment.concurrency_limit_id column that is a nullable FK to concurrency_limit_v2.id. The migration will try to backfill pre-existing data
• Updates deployment APIs (create/upsert, update, delete) to manage a related global concurrency limit object based on requested deployment.concurrency_limit int values
• Updates deployment API responses to include an expanded global_concurrency_limit object which includes the backing limit integer in addition to other fields like the underlying GCL's name
• Updates worker deployment-concurrency-limiting behavior to directly use the deployment's related GCL via the API response's nested GCL name rather than relying on an editable naming convention / upserting-at-runtime
• Updates runner deployment-concurrency-limiting behavior to directly use the deployment's related GCL via the API response's nested GCL name rather than relying on an editable naming convention / upserting-at-runtime
• Adds deprecation notes for:
  • the int-based deployment.concurrency_limit DB column is now deprecated. The column still exists for now and is being written to but no longer read.
  • the int-based deployment.concurrency_limit API response field is now deprecated. This field will still be returned from deployment APIs, but it will always be None for client-side compatibility.
  • the int-based DeploymentConcurrencyLimitFilter for filtering deployments via the /filter API. This still exists so as to not 422 on clients using this filter, but the filter will have no effect.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

[codspeed-hq]

CodSpeed Performance Report

Merging #15426 will not alter performance

_{Comparing deployment-concurrency/improve-deployment-gcl-mgmt (9a75b80) with main (bb96af8)}

Summary

✅ 3 untouched benchmarks

[collincchoy]

Note that you can still access deployment.concurrency_limit but it's now deprecated so it emits a warning on access and also it will be None.

[desertaxle]

I have a couple of questions about if/when we'll be able to remove fields deprecated in this PR, but otherwise LGTM!